1. Field of the Invention
The present invention generally relates to a wrist exerciser that is held by a palm of a user and having an internal rotor that is caused to rotate by the user exercising his or her wrist muscles, and in particular to a wrist exerciser having a rotor structure that allows for exchange with other rotors having different weights.
2. The Related Art
Wrist exercisers are widely known in exercising and training wrist-related muscles, especially for rehabilitation and therapy purposes. An example of the wrist exercisers is illustrated in U.S. Pat. No. 5,800,311, which provides a device that allows a user to exercise his or her wrist by simply rotating the wrist exerciser with the wrist.
FIG. 10 of the attached drawings shows a conventional wrist exerciser, which is designated with reference character A, comprising a rotor A1 encased in a spherical casing constituted by upper and lower hemi-spherical casing members A2, A3. A circumferential groove A11 is defined around the rotor A1. A hole A12 is defined in the rotor A1 inside the groove A11. The upper casing member A2 defines an opening A21 substantially corresponding in position to the groove A11 for the extension of a rope B. The rope B is wound around the rotor A1 by being received in and extending along the groove A11. When the rope B is quickly withdrawn out of the rotor A1, the friction between the rope B and the rotor A1 causes the rotor A1 to rotate inside the casing.
In order to maintain proper rotation and induce force on the wrist of the user, the rotor A1 must be of a substantial weight. This is usually done by embedding a metal block or metal plate inside the rotor A1, which complicates the manufacturing process of the rotor A1 and increases manufacturing costs. In addition, such a rotor A1 has a fixed weight that cannot be readily changed to accommodate players of different strength. For example, an adult and a child may require rotors of different weight in order to avoid under-training or over-training.
Other known techniques provide rotors made by metal casting. To provide rotors of different weights, different molds are required. This apparently increases the manufacturing costs of the wrist exerciser. In addition, due to the conductivity of the metal rotors, the metal rotors do not allow directly mounting illuminating electronics that gives off light when rotating. Further, adding sensor for counting the turns of rotation to the metal rotors raises another problems for additional machining is needed.
Thus, it is desired to provide a wrist exerciser having a rotor that overcomes the above deficiencies of the conventional wrist exercisers.